A unique adventure for them and for the company, which has opened up a niche market through the size and precision of its components. The astronomers want the very best conditions for observing the stars. ALMA is the largest radio astronomical project in the world, situated on a unique site in the Atacama Desert on the Chajnantor Plateau, at an altitude of more than 5,000m. The site offers exceptional conditions: cloudless skies and very dry, clear air. Each antenna collects its share of radio waves which are then transmitted by cable to the permanent station, situated lower down at an altitude of around 2,900m. But the real speciality of ALMA is interferometry: the information produced by each antenna is ‘added up’, turning the 60 antennas into a single gigantic radio telescope with a size varying between 160 x 250m in a compact configuration to up to 15km in diameter, depending on the arrangement of the antennas.
The ALMA project is an international collaboration between Europe, Japan and North America in cooperation with Chile. (thanks to special vehicles, as each complete antenna weighs 100t). The European antennas are built by the AEM consortium (Alcatel Alenia Space, European Industrial Engineering SrL, MT Aerospace) and by their subcontractors including Duqueine. “It was a tough struggle to break into the market for the antenna reflector, because it is a prestigious European reference project. We landed it at the end of 2006,” says Jérôme Aubry, Head of Marketing and Sales at Duqueine, with pride.
At the heart of the antenna, the parabolic dish collects the radio waves and concentrates them on the receiver at the focal point. “The parabola has a diameter of 12m, a height of 3m and weighs 5t. The parabolic surface must not deviate from the ideal form by more than ±1.5mm. “Such precision is required as the brackets fo the micrometric control system are fixed to this surface,” explains Francis Sedeilhan, the project leader and initiator.
As soon as the contract was landed, work began. The parabola was defined geometrically (dimensions and tolerances) and functionally (rigidity, expansivity, and wind resistance for example) but it had to be designed in detail. The design office at Duqueine (around 30 engineers) tackled the job with a ‘design to cost’ approach. The material used is ACG carbon material with a very high modulus of 394 GPa. Molds had to be created on which the pre-cut panels were laid, and the production sequence had to be defined (cutting of carbon and assignment to kits, placing, baking temperature and cycle, cutting of pieces by water jet etc.). Each parabolic dish is assembled from 16 petals (slices), each created by gluing together 15 pieces. All assembly work is performed on a jig under the implacable eye of a FARO Laser Tracker X. For ease of transport, the reflector is divided into two semi-parabolas. This is the reason for the engineers’ trip to Chile. They have to ensure the two pieces fit perfectly… but for the first antenna only.
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